The 1971 San Fernando earthquake (also known as the Sylmar earthquake) occurred in the early morning of February 9 in the foothills of the San Gabriel Mountains in southern California. The list of items needing improvements included building codes, dams and bridges being made more earthquake resistant, hospitals that are designed to remain operational, and the restriction of development near known fault zones. As of 1973, a few of the highest risk (26 were completed in zone 3 alone) sites that had been completed were in Seattle, Memphis, Charleston, and Boston. The group of one-story structures 300 feet west of the new facility, and some other buildings, were not damaged. More than 400 portable classrooms and 53 wood frame pre-Field Act buildings were also in use. [21], The upper dam was constructed in 1921 with the hydraulic fill process, three years after the larger lower dam, which was fabricated using the same style. As one portion of the study, Dick Saul mapped in detail the southeast quarter of the Oat Mountain 71/2-minute quadrangle, through which the Santa Susana thrust fault cuts obliquely. Because the first floor almost collapsed, the building was leaning to the north by almost two feet, and three of the four concrete stair towers fell away from the main building. It is evident, however, that more faults in the San Fernando Valley area may be active today than are now recognized." The main building was demolished at a cost of $127,000, and none of the various post-Field Act buildings were damaged at the site. Following the San Fernando event, earthquake engineers and seismologists from established scientific organizations, as well as the newly formed Los Angeles County Earthquake Commission, stated their recommendations that were based on the lessons learned. Though the reinforced concrete block structure was afflicted by the shock and uplift, the relatively good performance was in stark contrast to that of the Olive View and Veterans Hospital complexes. Northridge, CA Earthquake 1994 - Miscellaneous Pictures - … The earthen lip of the dam fell into the reservoir and brought with it the concrete lining, while what remained of the dam was just 5 feet (1.5 m) above the water level. In the city of San Fernando, underground water, sewer, and gas systems suffered breaks too numerous to count, and some sections were so badly damaged that they were abandoned. The event was one in a series that affected the Los Angeles area in the late … 100% satisfaction guaranteed. After the M6.4 1933 Long Beach earthquake the Field Act was passed the following month, and after the 1989 Loma Prieta earthquake, the Seismic Hazards Mapping Act and Senate Bill 1953 (hospital safety requirements) were established. University Library Contributing Institution California State University, Northridge Collection San Fernando Valley History Rights Information The unincorporated districts of Newhall, Saugus, and Solemint Junction had moderate damage, even to newer buildings. Most of the masonry and reinforced concrete buildings constructed after 1933 withstood the shaking and most did not collapse, but in 1972 a resolution came forth to abandon the site and the remaining structures were later demolished, the site becoming a city park. Unlike the situation at the Antelope Valley Interchange, permanent ground movement (defined as several inches of left-lateral displacement with possibly an element of thrusting) was observed in the area. Among those attending, in addition to Division personnel, were representatives from the California Institute of Technology, the U S. Geological Survey, the National Ocean Survey (a part of the National Oceanic and Atmospheric Administration), the University of California at Santa Barbara, the University of Southern California, California State College at Los Angeles, and the University of Washington; from several state agencies-the Division of Oil and Gas, the Division of Highways, the Department of Water Resources; from Los Angeles County and from Los Angeles City; as well as from several private consulting firms. While lateral, transverse, and vertical motions were all observed, the largest individual component of movement was 5 ft 3 in (1.60 m) of left lateral slip near the middle of the Sylmar segment. The fault that was responsible for the movement was not one that had been considered a threat, and this highlighted the urgency to identify other similar faults in the Los Angeles metropolitan area. By 1971, the facility comprised 45 individual buildings, all lying within 5 km (3.1 mi) of the fault rupture in Sylmar, but the structural damage was found to have occurred as a result of the shaking and not from ground displacement or faulting. Charlie Bishop came from San Francisco, as well as several staff members from Sacramento-Quint Aune, Chief Wes Bruer, Bob Matthews, and Bennie Troxel. Also known as the Sylmar Earthquake, this earthquake occurred on the San Fernando fault zone, a zone of thrust faulting which broke the surface in the Sylmar-San Fernando Area. The overall fault displacement was summarized by geologist Barclay Kamb and others as "nearly equal amounts of north–south compression, vertical uplift (north side up), and left lateral slip and hence may be described as a thrusting of a northern block to the southwest over a southern block, along a fault surface dipping about 45° north. Teleseismic P, SV, and SH waves recorded by the WWSS and Canadian networks from the 1971 San Fernando, California earthquake (M L = 6.6) are modeled in the time domain to determine detailed features of the source as a prelude to studying the near and local field strong-motion observations. The Los Angeles Unified School District had 660 schools consisting of 9,200 buildings at the time of the earthquake, with 110 masonry buildings that had not been reinforced to meet the new standards. Since both occurred in urban and industrial areas and resulted in significant economic impairment, each event drew critical observation from planning authorities, and has been thoroughly studied in the scientific communities. [19], On the grounds, there were cracks in the pavement and soil, but no surface faulting. [16], The areas that were affected by the strongest shaking were the outlying communities north of Los Angeles that are bounded by the northern edge of the San Fernando Valley at the base of the San Gabriel Mountains. The 1971 San Fernando Earthquake. Casualties in these highly affected areas might have increased had the shock occurred later in the day. [24], The large number of public school buildings in the Los Angeles area displayed mixed responses to the shaking, and those that were built after the enforcement of the Field Act clearly showed the results of the reformed construction styles. A preliminary report of their investigations is presented in this magazine. Ground displacement damaged sidewalks and roads, with cracks in the more rigid asphalt and concrete often exceeding the width of the shift in the underlying soil. The San Fernando earthquake has been extensively studied by many seismologists, geologists, and earthquake engineers. The earthquake that rocked the northern San Fernando Valley, near Sylmar measured magnitude 6.6 on the Richter magnitude scale. When it was apparent that the landslide potential of the hillsides, though great, did not threaten any urban areas, the geologists turned their attention to the study of geologic effects--so often ephemeral--and to other geologic hazards that may have been developed or increased by the earthquake. [19], The Veterans Administration Hospital entered into service as a tuberculosis hospital in 1926 and became a general hospital in the 1960s. The two geologists Carl Wentworth and Robert Yerkes from the US Geological Survey in Pasadena later wrote that "the San Fernando fault was discovered to be active only when it ruptured the ground surface on February 9, 1971. In the vicinity of the Sylmar Fault segment, there was a low possibility of landslides due to a lack of elevation change, but in the foothills and mountainous area a large amount of landsliding occurred and more work was necessary to eliminate the possibility of misidentifying a feature. The greatest damage was in the San Fernando area, near the front of the San Gabriel Mountains, where three hospitals were badly damaged (one of them accounting for the greatest loss of lives). As the plate shifted to the north, a portion of the terrane that was once parallel with the coast was rotated in a clockwise manner, which left it positioned in its east–west orientation. Huge collection, amazing choice, 100+ million high quality, affordable RF and RM images. Another result of the event involved the hundreds of various types of landslides that were documented in the San Gabriel Mountains. Nursing homes also were affected. An inspection of the lower dam in 1964 paved the way towards an arrangement between the State of California and the Los Angeles Department of Water and Power that would maintain the reservoir's water level that was reduced 10 feet lower than was typical. The frontal fault system at the base of the San Gabriel Mountains extends from the San Jacinto Fault Zone in the east to offshore Malibu in the west, and is defined primarily by moderate to shallow north-dipping faults, with a conservative vertical displacement estimated at 4,000–5,000 feet (1,200–1,500 m). The 1971 San Fernando earthquake with a 6.6 magnitude and large aftershocks caused over $500 million in damages and destruction to infrastructure; including the collapsed freeway overpasses on the Interstate freeways 5, 14, and 210, destruction of several hospitals in the North Los Angeles area, and damage to the Van Norman Dam in Granada Hills. [10], Several key attributes of the event were shared with the 1994 Northridge earthquake, considering both were brought about by thrust faults in the mountains north of Los Angeles, and each resulting earthquake being similar in magnitude, though no surface rupture occurred in 1994. Schools were affected, as they had been during the 1933 Long Beach earthquake, but this time amended construction styles improved the outcome for the thousands of school buildings in the Los Angeles area. Accentuated damage near alluvium had been documented during the investigation of the effects of the 1969 Santa Rosa earthquakes. An hour before sunrise, at 6:01 AM, PST, on February 9, 1971, the San Fernando region was struck by one of the most devastating earthquakes in California history. Transportation around the Los Angeles area was severely afflicted with roadway failures and the partial collapse of several major freeway interchanges. The 1971 San Fernando earthquake, also known as Sylmar earthquake, struck the San Fernando Valley near Sylmar at 6:00:55 a.m. PST on February 9, 1971… the 1971 san fernando earthquake An hour before sunrise, at 6:01 AM, PST, on February 9, 1971, the San Fernando region was struck by one of the most devastating earthquakes in California history. The Antelope Valley Freeway had damage from Newhall Pass to the northeast, primarily from settling and alignment issues, as well as splintering and cracking at the Santa Clara River and Solemint bridges. The structure had been built according to earthquake-resistant code provisions; mapped faults, as shown by Dr. Oakeshott on his San Fernando quadrangle, were considered in the engineering design. It was California's third worst earthquake in terms of lives lost (exceeded by San Francisco, 1906 and Long Beach, 1933) and second in terms of property damage (exceeded by San Francisco, 1906). [27], California Strong Motion Instrumentation Program, Prior to the San Fernando earthquake, some structural engineers had already believed that the existing groundwork for seismic design required enhancement. The Transverse Ranges form the perimeter of a series of basins that begins with the Santa Barbara Channel on the west end. The areas that were affected by the strongest shaking were the outlying communities north of Los Angeles that are bounded by the northern edge of the San Fernando Valley at the base of the San Gabriel Mountains. This made the earthquake the most documented event, at the time, in terms of strong-motion seismology; by comparison, the 1964 Alaska earthquake did not provide any strong motion records. The upstream slope of Lower San Fernando Dam failed during the 1971 San Fernando earthquake (Seed et al. The unanticipated thrust earthquake had a magnitude of 6.5 on the M s scale, and a maximum Mercalli intensity of XI (Extreme).The event was one in a series that affected the Los Angeles area in the late … Analysis revealed that the earthquake triggered over 1,000 landslides. Shear cracking occurred at the column closest to the western abutment, and the ground at the same column's base exhibited evidence of rotation. The death toll of this earthquake was about 58, but the property damage was enormous. Intact blocks of embankment material moved tens of feet on liquefied hydraulic fill shell material (figures D-8-1 and D-8-2). The initial surveyors of the extensive faulting in the valley, foothills, and mountains reported only tectonic faulting, while excluding fissures and other features that arose from the effects of compaction and landsliding. The two facilities, located near Grapevine and Weldon canyons that channel water and debris off the Sierra Madre Mountains, are lined by steep ridges and have formed alluvial fans at their mouths. The greatest number of slides were centered to the southwest of the mainshock epicenter and close to the areas where surface faulting took place. The Olive View Medical Center and Veterans Hospital both experienced very heavy damage, and buildings collapsed at both sites, causing the majority of deaths that occurred. On the day following the earthquake, State Geologist Wesley Bruer convened a meeting of more than 40 geologists and seismologists engaged in studying the earthquake, so that all investigative activities might be coordinated. "[14], The USGS commissioned a private company and the United States Air Force to take aerial photographs over 97 sq mi (250 km2) of the mountainous areas north of the San Fernando Valley. 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